The invention relates to a synchronizing cylinder assembly incorporating equal displacement hydraulic cylinders.
Multiple lifters using hydraulic or pneumatic cylinders are used in a variety of environments. The lifters may be used to raise and lower vehicles in service stations and repair centers as well as being used in robotics and assembly line production. In the case of an assembly line, multiple lifters may be required to vertically or laterally move a manufactured part simultaneously and at the same rate. It is often critical that the multiple lifters and the associated cylinders maintain the same extension during the manufactured process even when the load on the lifters or cylinders are unequal. Synchronizing cylinders assemblies have often used single rod cylinders.
The use of single rod cylinders has always had one drawback, being that the cylinder has a different volume displacement from the extension of the cylinder rod to the retraction of the cylinder rod. This is due to the rod diameter on one side of the piston, which makes the use of cylinders for the synchronizing of multiple units very difficult. Thus, other cylinder types have been developed.
First, there is the double rod cylinder, which equalizes the displacement with a rod on both sides of the piston. However, this creates a space issue. The design must now incorporate extra room for the cylinder rod that extends out the opposite end of the cylinder.
Second, there is the rodless cylinder. This cylinder has a carriage for mounting, as opposed to a threaded rod end, which is either mechanically or magnetically coupled to the piston. This design also has a drawback. The magnetically coupled carriage can be uncoupled from the piston while the mechanism is functioning. This uncoupling can cause machine failure or even extreme damage to the machine, while the mechanically coupled unit is prone to leakage and is not suitable for a hydraulic application.
It is the intent of the present invention to address the aforementioned concerns. According to the invention a close circuit synchronizing cylinder assembly is provided for synchronizing at least two external devices having a movable member with reciprocal movement such that the devices move at the same rate and stay level to each other within a small deviation throughout the cyclic movements of the movable members. In one aspect of the invention the synchronizing cylinder assembly includes a hydraulic cylinder for each external device wherein each hydraulic cylinder communicates with the other hydraulic cylinder in a closed circuit system. The hydraulic cylinder includes a piston slidable within the hydraulic cylinder and a piston rod projecting from a rod end of the cylinder. The interior of the cylinder is divided into 3 chambers. The rod outer diameter, rod inner diameter and cap end chambers. The rod outer diameter chamber and the rod inner diameter chamber encapsulate hydraulic fluid, while the third chamber is open to atmosphere. Multiple cylinders communicate with each other such that the hydraulic fluid in the rod outer diameter chamber of one cylinder communicates with hydraulic fluid in the rod inner diameter chamber in another cylinder.
In another aspect of the invention the synchronizing cylinder assembly includes a means for communicating fluid from the third chamber of the cylinder to a reservoir assembly. The reservoir assembly includes an inside chamber with an exhaust port open to atmosphere and means for directing hydraulic fluid that passes through seals into the third chamber, to a rod outer diameter chamber or rod inner diameter chamber of the cylinder.
In a further aspect of the invention, the cylinder has a means of bleeding air from the cylinder.
In another aspect, the cylinder includes an equalizing vent communicating between the rod outer diameter chamber and the rod inner diameter chamber to allow minimal fluid to pass therethrough to compensate for any seal leakage that would otherwise prevent full cylinder stroke.